【例2】 One Friday, we were packing to leave for a weekend away _____my daughter heard cries for help.
A. after B. while C. since D. when
答案：D。
點撥：此題中就用了以上第①種句式，表示“某人正在做某事，這時突然……”，整句意為“某一個星期五，我們正在收拾行李準(zhǔn)備外出度周末，這時我女兒突然聽到呼救聲”。
此外，when還可表“既然”之意。如：It was foolish of you to take a taxi when you could easily walk there in five minutes. 既然你五分鐘之內(nèi)能走到那兒，你還乘出租車，真是太傻了。
（2）while作為從屬連詞還可表示“雖然，盡管”之意。
【例3】______volleyball is her main focus, she’s also great at basketball.
A. Since B. Once C. Unless D. While
答案：D。
點撥：此題句意為 “雖然排球是她的主要項目，但她也擅長籃球”。其中while意為“雖然，盡管”。
2.till/until的兩種句式
表二：till與until的區(qū)別
| 連詞 | 意義 | 用法 | 從句謂語動詞特點 |
| till/until | 一直到……為止 | 主句和從句都用肯定形式 | 主句的動詞為延續(xù)性動詞 |
| not…till/until | 直到……才 | 主句用否定式，從句用肯定式 | 主句的動詞為非延續(xù)性動詞 |
如：
I’ll stay here till/until the rain stops.
He didn’t go home till/until he finished his homework.
【例4】 If a lot of people say a film is not good, I won’t bother to see it, or I’ll wait ______ it comes out on DVD.
A. whether B. after C. though D. until
答案：D。
點撥：此題從句意看，應(yīng)表示“如果許多人說某一部影片不好，我就不會費(fèi)神去看了，或者我會等到DVD出來”。所以要用until表示“直到……”之意，故選D。
【注意】till 不可置于句首，而until可置于句首；not until置于句首時主句要倒裝。如：Not until he came back did we know that he had been away for three weeks.
not until也可用在It is…that…的強(qiáng)調(diào)結(jié)構(gòu)中，但這時要把not until一起提前，而且不需要倒裝。如：She won’t go to bed until he returns home. 在強(qiáng)調(diào)結(jié)構(gòu)中應(yīng)是這樣的：It is not until he returns home that she will go to bed.
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